1. Field of the Invention
The present invention relates to a flip-flop circuit that latches inputted data.
2. Description of the Related Art
A reduction in power consumption is required for an LSI (Large Scale Integration) mounted on electronic equipment. In particular, the reduction in power consumption is strongly required for LSIs mounted on battery-driven mobile devices for the purpose of securing the extended battery life. A large portion of electric power consumed within the LSI is consumed as power for the charging and discharging of gate capacitances used for turning on and off gates of transistors by clock signals. Thus, the reduction in power consumed by the charging and discharging will be effective in the reduction of power consumed by LSIs.
The aforementioned power consumed by the charging and discharging by the clock signals is proportional to the square of power supply voltage. Thus, the reduction in the amplitude of clock signal will be effective in the reduction of power consumed by the charging and discharging.
FIG. 1 shows a flip-flop circuit that operates by a low-amplitude clock. Referring to FIG. 1, the amplitude of a clock signal clk and its inverted clock signal clkb is reduced to one half (Vcc/2) of a power supply voltage Vcc.
When a gate of a transistor is to be turned on and off using a low-amplitude signal, the current drive capacity of the transistor deteriorates and the transistor operates slower as compared with a case where the transistor is turned on and off using the full-amplitude signal. The size of a transistor, more specifically the gate width thereof, needs to be increased in order to make the operating speed of the transistor faster by using the low-amplitude signal. However, such a transistor requires a large electric power for the charging and discharging of gate capacitance. Thus, if the aforementioned power consumed by the charging and discharging is to be suppressed and reduced using low-amplitude clocks, the size of transistor must be increased or slower operating speed thereof must be tolerated.